Fuel cell system

Abstract

The invention relates to a fuel cell system. When the system is started, the fuel cell system supplies an oxidant gas and executes a fuel pre-injection step in which the fuel gas is supplied at a supply flow rate of the fuel gas at which the fuel concentration of the combustion unit is equal to or less than the lower limit of explosion with respect to the supply flow rate of the oxidant gas. And an ignition step in which the combustion unit is ignited until the concentration of oxygen remaining in the fuel line from the fuel supply system to the combustion unit is equal to or less than a predetermined concentration.

Description

Technical Field

[0001] The present invention discloses a fuel cell system. Background Art

[0002] A fuel cell system of this type has been proposed, for example, one comprising a reformer, a solid oxide fuel cell, a fuel manifold for collecting gases passing through the solid oxide fuel cell, a combustion section for combusting gases discharged from the fuel manifold, and an igniter for igniting the combustion section (see, for example, Patent Document 1). In this system, during startup, after a pre-purge to exhaust various gases remaining within the system by supplying generator air and reforming air, fuel supply is initiated, replacing the air remaining in the fuel manifold with a high-concentration fuel exceeding the upper limit of the fuel's flammable range. Subsequently, reforming air supply is initiated, igniting the gases discharged from the fuel manifold into the combustion section.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-207413

[0004] In the above-mentioned fuel cell system, if the fuel concentration deviates from the target concentration due to tolerances in auxiliary equipment or control, there is a concern about flashback from the combustion unit to the fuel line. While the use of a flashback prevention device is being considered, it would increase costs. Furthermore, in a fuel cell system composed of multiple connected power generation modules, each containing one or more fuel cell stacks, if fuel gas is uniformly supplied to each power generation module during system startup and ignition using a burner, there is a concern that flashback may occur in some power generation modules due to insufficient fuel gas. While the use of a flashback prevention device is being considered, it would increase costs. Summary of the Invention

[0005] The main purpose of the fuel cell system of the present invention is to ignite the combustion unit at low cost and more safely when the system is started.

[0006] The fuel cell system of the present invention adopts the following mechanism to achieve the above-mentioned main object.

[0007] The fuel cell system of the present invention is mainly composed of:

[0008] A fuel cell stack that generates electricity through the reaction of fuel gas and oxidant gas; a combustion unit that burns a mixture of residual fuel gas and residual oxidant gas from the above-mentioned fuel cell stack; an igniter that is used for igniting the above-mentioned combustion unit; a shell that has heat insulation properties and accommodates the above-mentioned fuel cell, the above-mentioned combustion unit and the above-mentioned igniter; a fuel supply system that supplies fuel gas to the above-mentioned fuel cell stack; an oxidant gas supply system that supplies oxidant gas to the above-mentioned fuel cell stack; and a control unit that supplies the above-mentioned oxidant gas when starting the system and performs a fuel pre-feeding process in which the above-mentioned fuel gas is supplied at a supply flow rate of the above-mentioned fuel gas at which the fuel concentration in the above-mentioned combustion unit becomes below the lower explosion limit relative to the supply flow rate of the above-mentioned oxidant gas, until the residual oxygen concentration in the fuel pipeline from the above-mentioned fuel supply system to the above-mentioned combustion unit becomes below a specified concentration, and then an ignition process for igniting the above-mentioned combustion unit is performed.

[0009] In the fuel cell system of the present invention, during system startup, a fuel pre-feed process is performed, in which fuel gas is supplied at a rate such that the fuel concentration in the combustion unit falls below the lower explosion limit, and until the residual oxygen concentration in the fuel line from the fuel supply system to the combustion unit falls below a predetermined concentration. Consequently, when the combustion unit is subsequently ignited, flame flashback to the fuel line is prevented, allowing the burner to be ignited safely. Furthermore, dedicated equipment such as a flashback prevention device is not required, resulting in cost reductions. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic diagram of the structure of the fuel cell system according to this embodiment.

[0011] Figure 2 It is a simplified structural diagram of multiple power generation units including power generation modules and auxiliary equipment.

[0012] Figure 3 This is a simplified structural diagram of the power generation module.

[0013] Figure 4 This is a flowchart showing an example of the startup process.

[0014] Figure 5 This is a flowchart showing an example of the hydrogen pre-charging step process.

[0015] Figure 6A 、 Figure 6B This is an explanatory diagram showing an example of the required replacement amount, hydrogen injection time, air flow rate, and hydrogen flow rate for each power generation module in the hydrogen preliminary injection step at the initial startup.

[0016] Figure 7It is an explanatory diagram showing how the hydrogen flow rate and the cumulative hydrogen flow rate of each power generation module change with time in the hydrogen pre-injection step.

[0017] Figure 8 This is an explanatory diagram showing an example of a required replacement amount acquisition map used when the system is restarted.

[0018] Figure 9 This is an explanatory diagram showing an example of the required replacement amount, hydrogen injection time, air flow rate, and hydrogen flow rate for each power generation module in the hydrogen preliminary injection process at the time of restart.

[0019] Figure 10 This is a flowchart showing the hydrogen pre-charging step processing according to another embodiment.

[0020] Figure 11 It is an explanatory diagram showing how the hydrogen flow rate and the cumulative hydrogen flow rate change over time for each power generation module in the hydrogen pre-injection step according to another embodiment.

[0021] Figure 12 This is a flowchart showing the hydrogen pre-charging step processing according to another embodiment.

[0022] Figure 13 This is a flowchart showing an example of the first ignition process.

[0023] Figure 14 This is a flowchart showing an example of the second ignition process.

[0024] Figure 15 This is a schematic diagram showing the structure of a fuel cell system according to another embodiment.

[0025] Figure 16 It is a schematic structural diagram showing a power generation module according to another embodiment. DETAILED DESCRIPTION

[0026] Modes for carrying out the present invention will be described with reference to the accompanying drawings.

[0027] Figure 1 is a simplified structural diagram of the fuel cell system 10 of this embodiment. Figure 2 is a simplified structural diagram of a plurality of power generation units 11 including power generation modules 20 and auxiliary equipment 30, Figure 3 2 is a simplified structural diagram of the power generation module 20 .

[0028] like Figure 1 As shown, the fuel cell system 10 of the embodiment includes a plurality of power generation units 11 and a unified control device 100 that manages the plurality of power generation units 11 .

[0029] like Figure 1 、2 As shown, each of the plurality of power generation units 11 includes a power generation module 20 including a fuel cell stack 21 and various auxiliary equipment 30 required for operating the fuel cell stack 21 , and a module control device 90 for controlling the various auxiliary equipment 30 .

[0030] like Figure 3 As shown, the power generation module 20 includes a fuel cell stack 21, a burner 22, and heat exchangers 23 and 24, which are housed in a heat-insulating module housing 29. Various auxiliary equipment 30 include a fuel supply system 40, an air supply system 50, a circulation system 60, a waste heat recovery system 70, etc. (see Figure 2 ).

[0031] The fuel cell stack 21 includes a plurality of solid oxide-type cells, each of which includes an electrolyte composed of stabilized zirconium oxide (e.g., YSZ), a fuel electrode composed of a composite of a catalyst metal such as Ni and stabilized zirconium oxide, etc., arranged on one side of the electrolyte, and an air electrode such as LSCF, arranged on the other side of the electrolyte. Each fuel cell stack 21 generates electricity through the reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas (air). A temperature sensor 25 is provided near the fuel cell stack 21. The temperature sensor 25 detects a temperature related to the temperature of the fuel cell stack 21 (stack temperature Tst).

[0032] like Figure 3 As shown, one end of a fuel gas supply pipe 21a is connected to the fuel electrode inlet of the fuel cell stack 21, and the other end of this fuel gas supply pipe 21a is connected to a fuel supply system 40. Furthermore, a heat exchanger 23 is provided on the fuel gas supply pipe 21a for performing heat exchange between the fuel gas flowing through the fuel gas supply pipe 21a from the fuel supply system 40 and the fuel electrode exhaust gas discharged from the fuel electrode outlet of the fuel cell stack 21. One end of an oxidant gas supply pipe 21b is connected to the air electrode inlet of the fuel cell stack 21, and the other end of this oxidant gas supply pipe 21b is connected to an air supply system 50. Furthermore, a heat exchanger 24 is provided on the oxidant gas supply pipe 21b for performing heat exchange between the oxidant gas flowing through the oxidant gas supply pipe 21b from the air supply system 50 and the combustion exhaust gas discharged from the burner 22.

[0033] The fuel electrode outlet of the fuel cell stack 21 is connected to a fuel electrode exhaust pipe 62. The fuel electrode exhaust pipe 62 is routed so as to pass through the heat exchanger 34. The oxidant gas electrode outlet of the fuel cell stack 21 is connected to the burner 22 via the oxidant gas electrode exhaust pipe.

[0034] The burner 22 is provided with an igniter 27 to combust the mixed gas of the fuel electrode exhaust and the oxidant gas electrode exhaust introduced into the burner 22. The combustion exhaust gas generated by the combustion of the mixed gas in the burner 22 passes through the heat exchanger 24 and is discharged outside the module housing 29. The burner 22 is provided with a temperature sensor 26 for detecting the temperature of the combustion area within the burner 22 (burner temperature Tf).

[0035] Hydrogen gas supplied as fuel gas by the fuel supply system 40 is introduced into the fuel electrode of the fuel cell stack 21 via the fuel gas supply pipe 21a, and air supplied as oxidant gas by the air supply system 50 is introduced into the air electrode of the fuel cell stack 21 via the oxidant gas supply pipe 21b. 2- ), the oxide ions pass through the electrolyte and react with hydrogen at the fuel electrode to obtain electrical energy. The fuel electrode exhaust that is not used for electrochemical reaction (power generation) in the fuel electrode of each single cell is subjected to heat exchange in the heat exchanger 23 with the fuel gas (hydrogen) supplied to the fuel electrode from the fuel supply system 40, and is then discharged to the outside of the module housing 29. In addition, the fuel electrode exhaust is supplied to the circulation system 60 through the fuel electrode exhaust piping 62, and after being cooled and the water vapor contained in the fuel electrode exhaust is removed by the condenser 61 provided in the circulation system 60, it is supplied to the burner 22 through the fuel electrode exhaust piping 63. In addition, the air electrode exhaust that is not used for electrochemical reaction (power generation) in the air electrode of each single cell is directly supplied to the burner 22. The fuel electrode exhaust introduced into the burner 22 is a combustible gas containing hydrogen, which is mixed with the air electrode exhaust containing oxygen introduced into the burner 22, and the mixed gas is burned in the burner 22, thereby maintaining the fuel cell stack 21 at an appropriate temperature by the combustion heat. Furthermore, the burner 22 generates combustion exhaust gas, which exchanges heat with air supplied to the air electrode from the air supply system 50 in the heat exchanger 24 and is then supplied to the waste heat recovery system 70 through the combustion exhaust gas piping 72. After the waste heat is recovered by the waste heat recovery system 70, the combustion exhaust gas is discharged to the outside air.

[0036] The fuel supply system 40 has: a hydrogen supply pipe 31 connected to a hydrogen supply source such as a hydrogen tank at one end, a branch pipe 41 branching from the other end of the hydrogen supply pipe 31 to each power generation module 20, and a hydrogen blower 42 respectively provided on each branch pipe 41. By operating the hydrogen blower 42, the hydrogen in the hydrogen tank 2 is pressurized (supplied) to the power generation module 20. The hydrogen blower 42 is respectively provided on each branch pipe 41, so each hydrogen blower 42 is independently controlled, thereby being able to control the supply amount of hydrogen per power generation module 20. In addition, an on-off valve 32 (double valve), a negative pressure prevention valve (not shown), etc. are provided on the hydrogen supply pipe 31. In addition to the hydrogen blower 42, a zero regulator 43 (equalizing valve), a flow sensor 44, etc. are also provided on each branch pipe 41. The flow sensor 44 detects the flow rate (fuel flow rate Fg) per unit time of the hydrogen (fuel gas) flowing in the branch pipe 41. The hydrogen gas introduced into the power generation module 20 is heated by heat exchange with the fuel electrode exhaust gas in the heat exchanger 23 and then supplied to the fuel electrode of the fuel cell stack 21 .

[0037] The air supply system 50 includes an air supply pipe 51 connected to each power generation module 20, a filter 52 installed at the inlet of each air supply pipe 51, and an air blower 53 installed in each air supply pipe 51. The air blower 53 is activated to draw air from the filter 52 and pressure-feed (supply) the drawn air to the power generation module 20. Since each air blower 53 is installed in each air supply pipe 51, each air blower 53 can be independently controlled, thereby controlling the air supply rate for each power generation module 20. Furthermore, a flow rate sensor 54 is installed in each air supply pipe 51. The flow rate sensor 54 detects the flow rate per unit time (air flow rate Fa) of the air flowing through the air supply pipe 51. The air introduced into the power generation module 20 is heated by heat exchange with the combustion exhaust gas in the heat exchanger 24 and then supplied to the air electrode of the fuel cell stack 21.

[0038] The circulation system 60 includes a condenser 61 having a separate heat exchange flow path for each power generation module 20; a fuel electrode exhaust pipe 62 having one end connected to each power generation module 20 (on the fuel electrode side of the fuel cell stack 21) and the other end connected to the inlet of each heat exchange flow path of the condenser 61; a fuel electrode exhaust pipe 63 having one end connected to the outlet of each heat exchange flow path of the condenser 61 and the other end connected to each power generation module 20 (on the burner 22 side); a circulation pipe 64 connecting the condenser 61 and a heat utilization device; and a circulation pump 65 provided in the circulation pipe 64. The fuel electrode exhaust discharged from the fuel electrode side of the fuel cell stack 21 is operated by the circulation pump 65 to exchange heat with the heat exchange medium circulating in the circulation pipe 64. After water vapor contained in the fuel electrode exhaust is removed in the condenser 61, the exhaust is supplied to the burner 22.

[0039] Further, the circulation system 60 is provided with a return pipe 66 branched from the fuel electrode exhaust pipe 63 on the downstream side of the condenser 61 and connected between the hydrogen blower 42 and the zero adjuster 43 of the branch pipe 41 of the fuel supply system 40, and an adjustment valve 67 (solenoid valve) provided in the return pipe 66. By opening the adjustment valve 67, a part of the fuel electrode exhaust passing through the condenser 61 can be returned to be supplied from the fuel supply system 40 to the power generation module 20. Further, instead of the adjustment valve 67, a hole can be provided in the return pipe 66.

[0040] The waste heat recovery system 70 is provided with a heat exchanger 71 connected to each combustion exhaust pipe 72, a heat storage tank 73, a circulation pipe 74 connecting the heat exchanger 71 and the heat storage tank 73, and a circulation pump 75 provided in the circulation pipe 74. By operating the circulation pump 75, combustion exhaust supplied to the heat exchanger 71 exchanges heat with a heat exchange fluid in the heat storage tank 73, and waste heat of the combustion exhaust is recovered by the heat storage tank 73. In addition, the waste heat recovery system 70 is further provided with a circulation pipe 76 connecting the heat storage tank 73 and a heat utilization device provided in a factory or the like, and a circulation pump 77 provided in the circulation pipe 76. By operating the circulation pump 77, heat recovered to the heat storage tank 73 can be supplied to the heat utilization device.

[0041] The fuel cell stacks 21 provided in the plurality of power generation units 11 are connected in series with a single power conditioner 15, and direct current generated in each fuel cell stack 21 is converted by the power conditioner 15 and supplied to a load L. A voltage sensor 91 for detecting the output voltage of the fuel cell stack 21 is provided between the output terminals of the fuel cell stack 21 of each power generation module 20. In addition, a voltage sensor 92 for detecting the voltage (total voltage Vt) of each fuel cell stack 21 as a whole is provided between one terminal (fuel electrode terminal) of the fuel cell stack 21 disposed at one end and the other terminal (air electrode terminal) of the fuel cell stack 21 disposed at the other end in the fuel cell stacks 21 connected in series. Further, a current sensor 93 for detecting the current flowing in the power line in which the fuel cell stacks 21 are connected in series is provided.

[0042] The power conditioner 15 has a DC / DC converter and an inverter, which converts the direct current from each fuel cell stack 21 into alternating current of a voltage (e.g., AC200V) that can be interconnected with the system power supply and outputs it. A power supply substrate (not shown) is connected to the power conditioner 15. The power supply substrate converts the power from each fuel cell stack 21 into direct current suitable for driving various auxiliary devices 30, the module control device 90, and the unified control device 100 and supplies them. In addition, a cooling fan and a ventilation fan (not shown) for cooling the power conditioner 15 and the power supply substrate are arranged in the auxiliary equipment room where the power conditioner 15, the power supply substrate, etc. are arranged.

[0043] Each module control device 90, although not shown, is configured as a microprocessor centered around a CPU. In addition to the CPU, it also includes a ROM for storing processing programs, a RAM for temporarily storing data, input / output ports, and a communication port. Input signals such as the stack temperature Tst from a temperature sensor 25 located near the fuel cell stack 21 of the corresponding power generation module 20, the burner temperature Tf from a temperature sensor 26 located on the burner 22, the voltage V from a voltage sensor 91 located between the output terminals of the fuel cell stack 21, the fuel flow rate Qg from a flow rate sensor 44 located on the branch pipe 41 corresponding to the fuel supply system 40, and the air flow rate Qa from a flow rate sensor 54 located on the air supply pipe 51 corresponding to the air supply system 50 are input to each module control device 90 via the input ports. Furthermore, control signals for the hydrogen blower 42 corresponding to the fuel supply system 40, the air blower 53 corresponding to the air supply system 50, and the regulating valve 67 corresponding to the circulation system 60 are output from each module control device 90 via the output ports.

[0044] The unified control device 100 is configured as a microprocessor centered around a CPU 101. In addition to the CPU 101, it also includes a ROM 102 for storing processing programs, a RAM 103 for temporarily storing data, an EEPROM 104 as non-volatile memory, a timer (not shown), input / output ports, and a communication port (not shown). Input signals such as the total voltage Vt detected by the voltage sensor 92 and the current I from the current sensor 93 are input to the unified control device 100 via the input port. Furthermore, control signals for the on-off valve 32, the circulation pump 65 of the circulation system 60, and the circulation pumps 75 and 77 of the waste heat recovery system 70 are output from the unified control device 100 via the output port. Furthermore, the unified control device 100 is communicatively connected to each module control device 90 via a communication bus 12, exchanging control signals and data.

[0045] Next, the operation of the fuel cell system 10 of this embodiment configured as described above will be described.

[0046] When a request to start the fuel cell system 10 is received from the higher-level system, the unified control device 100 transmits a startup instruction to each module control device 90 to perform startup processing. The startup process includes an air purge step, a hydrogen pre-injection step, an ignition step (a first ignition step, a second ignition step), and a preheating step. Each module control device 90 sequentially executes each step according to the instruction from the unified control device 100. Furthermore, when each fuel cell stack 21 has completed preheating and is ready for power generation, the unified control device 100 transmits a power generation instruction to each module control device 90.

[0047] During power generation, each module control device 90 inputs the target fuel flow rate Fgtag and target air flow rate Fatag set by the unified control device 100 based on the required power of the system, and controls the corresponding hydrogen blower 42 and air blower 53 based on the input target values. Specifically, each module control device 90 drives and controls the hydrogen blower 42 through feedback control based on the difference between the target fuel flow rate Fgtag and the fuel flow rate Fg detected by the flow sensor 44, and drives and controls the air blower 53 through feedback control based on the difference between the target air flow rate Fatag and the air flow rate Fa detected by the flow sensor 54.

[0048] If the system is required to stop, each module control device 90 performs a stop process according to the instruction from the unified control device 100. During the stop process, each module control device 90 controls the hydrogen blower 42 in a manner to supply hydrogen at a flow rate that does not cause oxidation and degradation of the electrodes of the fuel cell stack 21, and controls the air blower 53 in a manner to supply air at a flow rate required for cooling the fuel cell stack 21. Moreover, if the stack temperature Tst from the temperature sensor 94 drops below a specified temperature, each module control device 90 stops the supply of fuel gas and air. If the system is stopped, the unified control device 100 starts measuring the elapsed time (system stop time). The system stop time is used for the hydrogen pre-injection process described later.

[0049] Furthermore, the details of the startup process will be described. Figure 4 1 is a flowchart showing an example of a startup process executed by the integrated control device 100. This process is executed when a request for startup of the fuel cell system 10 is made from a higher-level system.

[0050] During the startup process, after confirming that each power generation module 20 is in an operable state (step S100), the unified control device 100 opens the on-off valve 32 (step S102) to send various instructions to the module control device 90 of each power generation module 20 to perform the startup process.

[0051] The unified control device 100 first instructs each module control device 90 to supply air to purge the inside of the burner 22 (step S104). Each module control device 90 that receives the instruction executes the air purge process by controlling the corresponding air blower 53 at a predetermined air flow rate. The air purge process is executed before the burner temperature Tf from the temperature sensor 26 is less than the specified temperature α (for example, 200°C) and this state continues within a specified time. If the air purge process is completed, the unified control device 100 instructs each module control device 90 to execute the hydrogen pre-injection process if the hydrogen pre-injection process has not been completed (No in step S106). (Step S108). The hydrogen pre-injection process is a step for replacing residual oxygen (air) in the fuel gas piping (branch pipe 41, fuel gas supply pipe 21a, and fuel electrode exhaust pipes 62 and 63) from the hydrogen supply system 40 of each power generation module 20 to the burner 22 with hydrogen injected from the hydrogen supply system 40 before the hydrogen concentration reaches the upper explosion limit (75%) or above. This hydrogen pre-injection process is performed during the subsequent ignition process (first ignition process) when the igniter 27 is turned on to ignite the burner 22 to prevent the flame from flashing back into the fuel gas piping. Details of the hydrogen pre-injection process will be described later.

[0052] Once the hydrogen pre-feed process is complete, the unified control device 100 instructs each module control device 90 to perform the first ignition process (step S110). Each module control device 90 controls the hydrogen blower 42 and air blower 53 to supply hydrogen and air to the combustion zone of the burner 22 at a predetermined hydrogen concentration (e.g., a concentration near the lower combustion limit of hydrogen). It then activates the igniter 27 to ignite the fuel gas, thereby performing the first ignition process of partial combustion. Furthermore, each module control device 90 monitors changes in the burner temperature Tf and determines whether the first ignition process was successful, transmitting the determination result to the unified control device 100. Based on the determination results received from each module control device 90, the unified control device 100 determines whether to execute the first ignition process again (step S112). This determination is made based on whether a determination result indicating failure of the first ignition process is received from any module control device 90. If the unified control device 100 determines that the first ignition process should be re-executed, it instructs the module control device 90 of the corresponding power generation module 20 to execute the air purge process (step S104). Furthermore, after the hydrogen pre-injection process is completed (a "yes" in step S106), the unified control device 100 skips the hydrogen pre-injection process and instructs the module control device 90 of the corresponding power generation module 20 to re-execute the first ignition process (step S110). Furthermore, if the first ignition process fails in some power generation modules 20, the first ignition process can be re-executed only for the corresponding power generation modules 20, or it can be re-executed for all power generation modules 20.

[0053] Next, the unified control device 100 instructs each module control device 90 to perform a second ignition step (step S114). Each module control device 90 controls the hydrogen blower 42 and air blower 53 to supply hydrogen and air to the combustion zone of the burner 22 at a predetermined hydrogen concentration (a hydrogen concentration greater than the hydrogen concentration during the first ignition step), thereby executing the second ignition step to completely combust the fuel gas. Furthermore, each module control device 90 monitors changes in the burner temperature Tf to determine the success or failure of the second ignition step and transmits the determination result to the unified control device 100. Based on the determination results received from each module control device 90, the unified control device 100 determines whether to execute the second ignition step again (step S116). This determination is made based on whether a determination result indicating failure of the second ignition step is received from any module control device 90. If the unified control device 100 determines that the second ignition step should be executed again, it instructs the module control device 90 of the corresponding power generation module 20 to execute the second ignition step again (step S114).

[0054] Furthermore, the unified control device 100 instructs each module control device 90 to start a preheating process (step S118). Each module control device 90 sets the target fuel flow rate Fgtag and the target air flow rate Fatag and controls the hydrogen blower 42 and the air blower 53 in such a manner that the fuel cell stack 21 reaches a state capable of generating electricity, thereby performing the preheating process. In addition, each module control device 90 monitors the stack temperature Tst from the temperature sensor 25. If the stack temperature Tst reaches a predetermined preheating end temperature, a notification of the end of preheating is sent to the unified control device 100. If the unified control device 100 determines that a notification of the end of preheating has been received from all module control devices 90 (yes in step S120), it controls the power conditioner 15 to start a current scan and instructs each power generation module 20 to start power generation operation (step S122), thereby completing the startup process.

[0055] Next, the details of the hydrogen gas pre-introduction process performed in step S108 will be described. Figure 5 1 is a flowchart showing an example of the hydrogen pre-injection process. In the following, regarding the hydrogen pre-injection process, the fuel cell system 10 is taken as an example in which the power generation module 20 includes five power generation modules HM1 to HM5. Figure 6A 、 Figure 6B To explain.

[0056] In the hydrogen pre-injection process, the unified control device 100 determines whether this system startup is the first time (step S200). If the unified control device 100 determines that this system startup is the first time, it obtains the amount of hydrogen required to replace the residual oxygen (air) in the fuel gas pipeline from the hydrogen supply system 40 to the burner 22 with hydrogen before the hydrogen concentration becomes above the combustion upper limit (75%), that is, the required replacement amount (step S202) for each power generation module 20. The required replacement amount is determined as an amount corresponding to the piping length of the fuel gas pipeline of each power generation module 20. In this embodiment, the piping length (primary side piping length) from the branch pipe 41 to the hydrogen supply pipe 31 to the hydrogen blower 42 is different for each power generation module 20, and the piping length (secondary side piping length) from the hydrogen blower 42 to the burner 22 is unified in all power generation modules 20. The required replacement amount is pre-stored in ROM 102 for each power generation module 20 according to the piping length of each power generation module 20. The integrated control device 100 reads the required replacement amount of the corresponding power generation module 20 from ROM 102 to obtain the required replacement amount.

[0057] Once the unified control device 100 obtains the required replacement amount for each power generation module 20, it calculates the hydrogen injection time required for replacement of the required replacement amount per power generation module 20, assuming that the hydrogen injection flow rate is set so that the hydrogen concentration in the fuel region of the burner 22 becomes the lower flammable limit for hydrogen (4%) multiplied by a predetermined safety factor relative to the predetermined air injection flow rate (step S204). For example, if the air injection flow rate is set to 20 [NLM] and the safety factor is set to 0.5, the hydrogen injection flow rate becomes 0.4 [NLM], and the hydrogen injection time for power generation module HM1 with a required replacement amount of 6.0 [L] is as follows: Figure 6A Similarly, the hydrogen injection time for the power generation module HM1 requiring a replacement amount of 6.2 L becomes 15.5 min, the hydrogen injection time for the power generation module HM3 requiring a replacement amount of 5.8 L becomes 14.5 min, the hydrogen injection time for the power generation module HM4 requiring a replacement amount of 6.1 L becomes 15.25 min, and the hydrogen injection time for the power generation module HM5 requiring a replacement amount of 7.0 L becomes 17.5 min.

[0058] Next, the unified control device 100 sets the calculated maximum value of the hydrogen injection time as the execution hydrogen injection time shared by all power generation modules 20 (step S206). Figure 6B As shown in FIG. 1 , the maximum value of the hydrogen injection time of each power generation module HM1 to HM5 is 17.5 [min], so 17.5 [min] is set as the common hydrogen injection execution time for all power generation modules MH1 to MH5. Furthermore, the unified control device 100 divides the required replacement amount of each power generation module 20 by the common hydrogen injection execution time to calculate the execution hydrogen injection amount of each power generation module 20 (step S208). Figure 6B As shown, 17.5 [min] is set as the hydrogen injection execution time, so 0.3429 [NLM] is set as the hydrogen injection execution flow rate for power generation module HM1, which requires a replacement amount of 6.0 [L]. Similarly, 0.3543 [NLM] is set as the hydrogen injection execution flow rate for power generation module HM1, which requires a replacement amount of 6.2 [L]. 0.3314 [NLM] is set as the hydrogen injection execution flow rate for power generation module HM3, which requires a replacement amount of 5.8 [L]. 0.3486 [NLM] is set as the hydrogen injection execution flow rate for power generation module HM4, which requires a replacement amount of 6.1 [L]. 0.4 [NLM] is set as the hydrogen injection execution flow rate for power generation module HM5, which requires a replacement amount of 7.0 [L].

[0059] In this manner, if a common hydrogen injection time and a specific hydrogen injection flow rate are set for each power generation module 20, the unified control device 100 transmits a hydrogen pre-injection instruction, including the hydrogen injection time and flow rate, to the corresponding module control device 90 (step S210), thereby terminating the hydrogen pre-injection process. Upon receiving the hydrogen pre-injection instruction, each module control device 90 sets the hydrogen injection flow rate to the target fuel flow rate Fgtag. Before the hydrogen injection time has elapsed, the hydrogen blower 42 is controlled by feedback control to ensure that the fuel flow rate Fg from the flow sensor 44 matches the target fuel flow rate Fftag. This allows hydrogen to replace the air in the fuel gas line from the fuel supply system 40 of each power generation module 20 to the burner 22, preventing flame flashback to the fuel gas line during the next ignition process (first ignition process) when the burner 22 is ignited. In addition, the required replacement amount is obtained for each power generation module 20, and the execution hydrogen injection flow rate and execution hydrogen injection time are set according to the obtained required replacement amount, so that unnecessary fuel consumption can be suppressed. As mentioned above, the execution hydrogen injection time is the time shared by all power generation modules 20, so if Figure 7 As shown, the hydrogen pre-injection process ends at the same time in all power generation modules 20. Therefore, the ignition timing of the burner 22 in the first ignition process performed after the hydrogen pre-injection process can be made consistent in each power generation module 20, thereby more reliably preventing the occurrence of flashback.

[0060] If the unified control device 100 determines that this system startup is not the first time but a restart, it obtains the time that has passed since the last system stop (system stop time) (step S212). Next, the unified control device 100 infers the required replacement amount shared by all power generation modules 20 based on the obtained system stop time (step S214). Immediately after the system stops, the fuel gas pipeline from the fuel supply system 40 to the burner 22 becomes filled with hydrogen. Moreover, the hydrogen in the fuel gas pipeline is gradually replaced with air introduced from the combustion exhaust gas pipeline, etc. over time. Therefore, when the system is restarted, the unified control device 100 infers the required replacement amount required to replace the air that has been replaced by hydrogen with hydrogen again based on the system stop time. In this embodiment, the relationship between the system stop time and the required replacement amount is experimentally obtained in advance and stored in ROM102 as a required replacement amount mapping table. If the system stop time is given, the required replacement amount is inferred by deriving the corresponding required replacement amount from the mapping table. In Figure 8An example of a required replacement amount map is shown in . In this embodiment, the piping downstream of the hydrogen blower 42 (secondary-side piping) in the fuel gas piping has the same piping length as that of each power generation module 20. Therefore, the amount of air replaced by hydrogen in the fuel gas piping per unit time is assumed to be approximately the same in each power generation module 20. Therefore, when restarting the system, the unified control device 100 estimates the required replacement amount common to all power generation modules 20.

[0061] If the unified control device 100 infers the required replacement amount common to all power generation modules 20, then relative to the predetermined air injection flow rate, the hydrogen concentration in the fuel area of ​​the burner 22 is set to a hydrogen injection flow rate obtained by multiplying the lower combustion limit of hydrogen (4%) by a specified safety factor, and is set as the execution hydrogen injection flow rate common to all power generation modules 20 (step S216). Moreover, the unified control device 100 divides the required replacement amount common to all power generation modules 20 by the set execution hydrogen injection flow rate to calculate the execution hydrogen injection time common to all power generation modules 20 (step S218). For example, when the air injection flow rate is set to 20 [NLM] and the safety factor is set to 0.5, as shown in FIG. Figure 9 As shown, the hydrogen injection flow rate is 0.4 [NLM]. In addition, the required replacement volume is common to all power generation modules HM1 to HM5, so when the required replacement volume is 1.57 [L], the hydrogen injection time for power generation modules HM1 to HM5 is 3.925 [min].

[0062] In this manner, if a common hydrogen injection time and a hydrogen injection flow rate are set for each power generation module 20, the unified control device 100 transmits a hydrogen pre-injection instruction containing the hydrogen injection time and hydrogen at the hydrogen injection flow rate to the corresponding module control device 90 (step S210), thereby terminating the hydrogen pre-injection process. Thus, when the system is restarted, the required replacement amount is estimated based on the system downtime, and the hydrogen injection flow rate and hydrogen injection time are set accordingly. This reduces unnecessary fuel consumption and prevents flashback during ignition of the burner 22 by pre-injecting hydrogen.

[0063] In the above embodiment, when the system is initially started, the unified control device 100 sets the hydrogen injection flow rate for each power generation module 20 and the hydrogen injection time common to all power generation modules 20 based on the required replacement amount of each power generation module 20. However, the unified control device 100 may also set the hydrogen injection flow rate common to all power generation modules 20 and the hydrogen injection time for each power generation module 20. Figure 10This is a flow chart showing the hydrogen pre-injection process of another embodiment. Figure 10 The hydrogen gas is put into each process in advance, Figure 5 The same processing is assigned the same step number, and the description thereof is omitted due to duplication.

[0064] exist Figure 10 In the hydrogen pre-injection process, the unified control device 100 determines in step S200 that this system startup is the first time, and then if the required replacement amount of each power generation module 20 is obtained in step S202, the hydrogen concentration in the fuel area of ​​the burner 22 is set to the hydrogen injection flow rate of the concentration obtained by multiplying the lower combustion limit of hydrogen (4%) by the specified safety factor, and is set as the execution hydrogen injection flow rate shared by all power generation modules 20 (step S300). Moreover, the unified control device 100 divides the required replacement amount of each power generation module 20 by the common execution hydrogen injection flow rate to calculate the execution hydrogen injection time of each power generation module 20 (step S302). For example, when the air injection flow rate is set to 20 [NLM] and the safety factor is set to 0.5, as shown in FIG. Figure 6A As shown, the hydrogen injection flow rate is 0.4 [NLM], and the hydrogen injection time of each power generation module HM1, HM2, HM3, HM4, and HM5 is 15.0 [min], 15.5 [min], 14.5 [min], 15.25 [min], and 17.5 [min], respectively. Thus, as in the present embodiment, the air in the fuel gas pipeline from the fuel supply system 40 of each power generation module 20 to the burner 22 can be replaced by hydrogen, and the flame can be prevented from backfired to the fuel gas pipeline when the burner 22 is ignited in the next ignition process (first ignition process). In addition, the hydrogen injection flow rate and the hydrogen injection time are set according to the required replacement amount, so that unnecessary fuel consumption can be suppressed. In addition, in the hydrogen pre-injection process of other embodiments, the hydrogen injection time of each power generation module 20 is different. Therefore, as Figure 11 As shown, among the power generation modules HM1 to HM5, the module control device 90 of the power generation modules HM1 to HM4 whose execution hydrogen injection time is not the longest sets a value of 0 as the target fuel flow Fgtag and stops the supply of hydrogen if their respective execution hydrogen injection times have passed, and then stands by until the execution hydrogen injection time of the power generation module MH5 with the longest execution hydrogen injection time has passed.

[0065] In the above embodiment, the piping length of the piping (secondary piping) from the hydrogen blower 42 to the burner 22 is unified in all power generation modules 20. However, the piping length of the secondary piping may be different in some power generation modules 20. In this case, instead of Figure 5 ,implementFigure 12 The hydrogen is put into the process in advance. Figure 12 The hydrogen gas is put into each process in advance, Figure 5 The processing standards and step numbers of the same processing are the same, and their descriptions are omitted due to repetition.

[0066] exist Figure 12 During the hydrogen pre-injection process, after the unified control device 100 determines in step S200 that this system startup is not the first time, if the system downtime is obtained in the subsequent step S212, the required replacement amount is estimated based on the obtained system downtime for each power generation module 20 (step S400). As in the present embodiment, the unified control device 100 uses a required replacement amount map to estimate the required replacement amount. Since the piping length of the secondary side piping varies for each power generation module 20, a required replacement amount map is prepared for each power generation module 20 through preliminary experiments. Next, as in step S204, the unified control device 100 calculates the hydrogen injection time required for replacement of the required replacement amount for each power generation module 20, assuming that the hydrogen injection flow rate is set so that the hydrogen concentration in the fuel region of the burner 22 is the concentration obtained by multiplying the lower flammability limit (4%) for hydrogen by a predetermined safety factor (step S402). Next, the unified control device 100 sets the calculated maximum value of the hydrogen injection time as the common hydrogen injection execution time for all power generation modules 20, as in step S206 (step S404). Furthermore, the unified control device 100 calculates the execution hydrogen injection amount for each power generation module 20 by dividing the required replacement amount for each power generation module 20 by the common execution hydrogen injection time, as in step S208 (step S406). Thus, even if the secondary piping lengths of each power generation module 20 differ, unnecessary fuel consumption can be reduced during the hydrogen pre-injection process when the system is restarted, and air in the secondary piping can be replaced with hydrogen.

[0067] In the above embodiment, although the unified control device 100 sets the hydrogen injection execution time and hydrogen injection execution flow rate of the fuel supply system 40 of each power generation module 20, each module control device 90 can also separately set the hydrogen injection execution time and hydrogen injection execution flow rate of the corresponding fuel supply system 40.

[0068] Next, the first ignition process executed in step S110 and the second ignition process executed in step S114 will be described in more detail. Figure 13 1 is a flowchart showing an example of the first ignition process. The first ignition process is executed by each module control device 90 in response to an instruction from the integrated control device 100.

[0069] During the first ignition process, each module control unit 90 determines whether the first ignition process being executed is a re-execution (ignition retry) (step S1200). If each module control unit 90 determines that it is not an ignition retry, it then determines whether this system startup is the first time (step S1202). If each module control unit 90 determines that this system startup is the first time, it sets the incremental value to 0 (step S1204) and then sets the value obtained by adding the incremental value ΔFg1 to the initial value Fini1 as the target fuel flow rate Fgtag (step S1206). In this embodiment, the initial value Fini1 is determined in step S1208, described later, to be a hydrogen flow rate determined so that the hydrogen concentration in the burner 22 is less than the lower explosion limit (4%) relative to the air flow rate supplied from the air supply system 50. For example, it is a flow rate equivalent to 2% or 3% in terms of hydrogen concentration. Assuming this is the first time the system is started, the incremental value ΔFg1 is set to 0, and the initial value Fini1 is set to the target fuel flow rate Fgtag. Next, each module control device 90 controls the air blower 53 at a predetermined air flow rate to start air supply (step S1208), and controls the hydrogen blower 42 at the target fuel flow rate Fgtag to start hydrogen supply (step S1210). Furthermore, each module control device 90 activates the igniter 27 to ignite the hydrogen and air mixture introduced into the burner 22 (step S1212).

[0070] Next, each module control unit 90 inputs the burner temperature Tf from the temperature sensor 25 (step S1214), subtracts the previously input burner temperature (previous Tf) from the currently input burner temperature Tf, and calculates a temperature change ΔTf (= Tf - previous Tf) (step S1216). Each module control unit 90 then determines whether the calculated temperature change ΔTf is greater than a predetermined amount α1 (step S1218) and whether this state continues for a predetermined time β1 (step S1220). The predetermined amount α1 and the predetermined time β1 are thresholds for determining whether partial combustion of the hydrogen introduced into the burner 22 has occurred, and are experimentally determined values. If each module control unit 90 determines that the temperature change ΔTf is less than the predetermined amount α1, or if it determines that the state does not continue for the predetermined time β1 even though the temperature change ΔTf is greater than the predetermined amount α1, it then determines whether a predetermined determination time has elapsed (step S1222). If each module control device 90 determines that the determination time has not elapsed, the process returns to step S1214 and repeats steps S1214 through S1222. If each module control device 90 determines that the temperature change ΔTf is greater than or equal to the predetermined amount α1 before the determination time has elapsed and that this state continues for the predetermined time β1, the first ignition process (partial combustion) is determined to have been successful (step S1224). Furthermore, each module control device 90 records the current increment value ΔTg1 (here, a value of 0) in the EEPROM 104 (step S1226), terminating the first ignition process.

[0071] During the repetition of steps S1214 to S1222, if each module control device 90 determines in step S1222 that the determination time has elapsed, it determines that the first ignition process has failed (step S1228). Next, each module control device 90 accumulates the incremental value ΔFg1 of the hydrogen flow rate supplied from the hydrogen supply system 40 when the first ignition process is repeated (ignition retry) (step S1230). The incremental value ΔFg1 is accumulated, for example, by gradually increasing by 1% when converted to the hydrogen concentration within the combustor 22. Each module control device 90 then determines whether the value obtained by adding the incremental value ΔFg1 to the initial value Fini1 exceeds the upper limit value Fmax1 (step S1232). The process in step S1232 determines whether the hydrogen concentration within the burner 22 exceeds a predetermined upper limit (e.g., 4% of the lower explosion limit of hydrogen) when an ignition retry is performed using the target fuel flow rate Fgtag obtained by adding the incremental value ΔFg1 after the cumulative count. If each module control unit 90 determines that the value obtained by adding the incremental value ΔFg1 to the initial value Fini1 is below the upper limit Fmax1, it determines that an ignition retry is being performed (step S1234), terminating the first ignition process. In this case, as described above, the first ignition process is executed again after the air purge process is executed during the startup process.

[0072] If the first ignition process is executed again, each module control unit 90 determines in step S1200 that the first ignition process is being executed again (ignition retry). Therefore, in step S1230, the value obtained by adding the incremented value ΔFg1 after cumulative counting to the initial value Fini1 is set as the target fuel flow rate Fgtag (step S1206). Then, through the processes of steps S1208 to S1222, the first ignition process is executed again, and the success or failure of the first ignition process is determined. Furthermore, if the first ignition process is successful (step S1224), each module control unit 90 records the current incremented value ΔTg1 (here, the cumulative value) in the EEPROM 104 (step S1226), and the first ignition process ends. On the other hand, if the first ignition process fails (step S1228), each module control unit 90 repeatedly accumulates the incremental value ΔTg1 and executes the first ignition process again (ignition retry) until the first ignition process succeeds or the value obtained by adding the incremental value ΔFg1 to the initial value Fini1 exceeds the upper limit value Fmax1. During this repetitive process, if each module control unit 90 determines in step S1232 that the value obtained by adding the incremental value ΔFg1 to the initial value Fini1 exceeds the upper limit value Fmax1, it determines that some abnormality has occurred in the fuel cell system 10, shuts down the fuel cell system 10 (step S1236), and resets the incremental value ΔFg1 recorded in the EEPROM 104 to 0 (step S1238), terminating the first ignition process. In this way, even if the first ignition process fails, by gradually increasing the hydrogen supply to the burner 22 and repeating the first ignition process, the burner 22 can be safely and reliably ignited. Furthermore, even if the first ignition process is repeatedly executed, if the first ignition process is unsuccessful, the fuel cell system 10 is stopped, and thus the abnormality of the fuel cell system 10 can be appropriately addressed.

[0073] If the first ignition process is successfully executed again, the incremental value ΔFg1 accumulated during the re-execution of the first ignition process is recorded in EEPROM 104. The next time the system is started up, each module control unit 90 determines in step S1202 that this is not the first system startup and reads the incremental value ΔFg1 recorded in EEPROM 104 (step S1240). The value obtained by adding the read incremental value ΔFg1 to the initial value Fini1 is set as the target fuel flow rate Fgtag, and the first ignition process is executed. Consequently, the optimal incremental value ΔFg1 is determined with repeated system restarts, enabling more reliable execution of the first ignition process.

[0074] Next, the second ignition step will be described. Figure 14This is a flowchart illustrating an example of the second ignition process. The second ignition process is executed by each module control device 90 based on instructions from the unified control device 100. The same step numbers are assigned to the processes of the second ignition process that are identical to those of the first ignition process, and detailed descriptions thereof are omitted due to duplication.

[0075] During the second ignition process, if each module control unit 90 determines in steps S1200 and S1202 that the second ignition process being executed is not a retry (ignition retry) but rather the initial system startup, it sets the incremental value ΔFg2 to a value of zero (step S1204B) and then sets the value obtained by adding the incremental value ΔFg2 to the initial value Fini2 as the target fuel flow rate Fgtag (step S1206B). The initial value Fini2 is greater than the initial value Fini1 used for the first ignition process and is, for example, determined to be a hydrogen flow rate at which the hydrogen concentration in the combustion unit 22 reaches the lower explosion limit (4%) relative to the air flow rate. Next, each module control unit 90 supplies air at a predetermined air flow rate (step S1208) and hydrogen at the target fuel flow rate Fgtag (step S1210).

[0076] Next, each module control unit 90 inputs the burner temperature Tf and calculates the temperature change ΔTf (steps S1214 and S1216). Each module control unit 90 then determines whether the temperature change ΔTf is greater than a predetermined amount α2 (step S1218B) and whether the state continues for a predetermined time β2 (step S1220B). The predetermined amount α2 and the predetermined time β2 are thresholds used to determine whether the burner 22 has transitioned from partial combustion to complete combustion, and are experimentally determined values. If each module control unit 90 determines that the temperature change ΔTf is less than the predetermined amount α2, or that the temperature change ΔTf is greater than the predetermined amount α2 but the state does not continue for the predetermined time β2, it then determines whether a predetermined determination time has elapsed (step S1222). If each module control unit 90 determines that the determination time has not elapsed, it returns to step S1214 and repeats steps S1214 through S1222. If each module control unit 90 determines that the temperature change ΔTf is greater than or equal to the predetermined amount α2 before the determination time has elapsed and that this state continues for the predetermined time β2, it determines that the second ignition process (complete combustion) has succeeded (step S1224B). Furthermore, each module control unit 90 records the current increment value ΔTg2 (here, a value of 0) in the EEPROM 104 (step S1226B), terminating the second ignition process.

[0077] During the repetition of steps S1214 to S1222, if each module control device 90 determines in step S1222 that the determination time has elapsed, it determines that the second ignition process has failed (step S1228B). Next, each module control device 90 accumulates the incremental value ΔFg2 of the hydrogen flow rate supplied from the hydrogen supply system 40 when the second ignition process (ignition retry) is repeated (step S1230B). The incremental value ΔFg2 is accumulated, for example, by gradually increasing by 1% when converted to the hydrogen concentration within the combustor 22. Furthermore, each module control device 90 determines whether the value obtained by adding the incremental value ΔFg2 to the initial value Fini2 exceeds the upper limit value Fmax2 (step S1232B). The process in step S1232B determines whether the hydrogen concentration within the combustor 22 exceeds a predetermined upper limit concentration when the ignition retry is performed using the target fuel flow rate Fgtag obtained by adding the accumulated incremental value ΔFg2. This upper limit concentration can be, for example, a concentration (e.g., 9%) obtained by multiplying the lower explosion limit (18%) by a predetermined safety factor (e.g., 0.5). If each module control unit 90 determines that the value obtained by adding the incremental value ΔFg2 to the initial value Fini2 is less than the upper limit value Fmax2, it determines to perform an ignition retry (step S1234) and returns to step S1200. Since a positive determination is made in step S1200, each module control unit 90 sets the value obtained by adding the cumulative incremental value ΔFg2 to the initial value Fini2 as the target fuel flow rate Fgtag (step S1206B), and repeats steps S1208 to S1222 to execute the second ignition process again.

[0078] If the second ignition process succeeds (step S1224B), each module control unit 90 records the current increment value ΔTg2 (here, the value after the cumulative count) in the EEPROM 104 (step S1226B), terminating the second ignition process. If the second ignition process fails (step S1228B), each module control unit 90 repeats the following process: until the second ignition process succeeds or the value obtained by adding the increment value ΔFg2 to the initial value Fini2 exceeds the upper limit value Fmax2, the increment value ΔTg2 is increased by a predetermined value and the second ignition process is executed again (ignition retry). During the repetitive processing, if each module control unit 90 determines in step S1232B that the value obtained by adding the incremental value ΔFg2 to the initial value Fini2 exceeds the upper limit value Fmax2, it determines that some abnormality has occurred in the fuel cell system 10, shuts down the fuel cell system 10 (step S1236), resets the incremental value ΔFg2 recorded in the EEPROM 104 to 0 (step S1238B), and terminates the second ignition process. Thus, if the second ignition process fails, by gradually increasing the hydrogen supply to the burner 22 and repeating the second ignition process, the occurrence of explosions and deflagrations can be more reliably prevented, and ignition of the burner 22 can be successfully completed. Furthermore, even if the second ignition process is repeated, the fuel cell system 10 is shut down if the second ignition process fails, thereby enabling appropriate response to abnormalities in the fuel cell system 10.

[0079] If the second ignition process is successfully executed again, the incremental value ΔFg2 accumulated during the second ignition process is recorded in EEPROM 104. The next time the system is started up, each module control unit 90 determines in step S202 that this is not the first system startup and reads the incremental value ΔFg2 recorded in EEPROM 104 (step S1240B). The value obtained by adding the read incremental value ΔFg2 to the initial value Fini2 is set as the target fuel flow rate Fgtag, and the second ignition process is executed. Consequently, the optimal incremental value ΔFg2 is determined with repeated system restarts, enabling more reliable execution of the second ignition process.

[0080] Thus, in this embodiment, by sequentially executing the first ignition step (partial combustion) and the second ignition step (complete combustion) as the ignition steps, even if the fuel concentration in the burner 22 slightly varies due to tolerances in the auxiliary equipment 30 or control, it is possible to prevent the occurrence of explosions and deflagrations. As a result, the hydrogen and air mixture in the burner 22 can be ignited more safely and reliably.

[0081] In the above embodiment, each fuel cell stack 21 is a component that generates electricity through the reaction of hydrogen and oxygen contained in air. However, the fuel cell stack 21 may also be a reversible solid oxide cell stack, capable of an FC mode for generating electricity and an EC mode for generating hydrogen through electrolysis of high-temperature steam while receiving power from a power source. Furthermore, the power source may be a system power supply, renewable energy such as a solar power generator, or a battery.

[0082] Figure 15 is a simplified structural diagram of a fuel cell system 10B according to another embodiment. Figure 16 This is a simplified diagram of the structure of the power generation module 20. In a fuel cell system 10B according to another embodiment, the power generation module 20 includes, in addition to the fuel cell stack 21, burner 22, and heat exchangers 23 and 24, an evaporator 25, and other components. These components are housed in a thermally insulated module housing 29. Furthermore, the evaporator 25 may be equipped with a heater to supplement insufficient heat within the evaporator 25. Various auxiliary equipment 30 include, in addition to the fuel supply system 40, air supply system 50, circulation system 60, and waste heat recovery system 70, a water supply system 80, and other components.

[0083] The water supply system 80 includes a water tank 81 that stores water (raw water), a water supply pipe 82 connected to the water tank 81 at one end, branch pipes 83 branching from the other end of the water supply pipe 82 to each power generation module 20, and a water pump 84 installed in each branch pipe 83. The water pumps 84 are operated to pump (supply) the raw water in the water tank 81 to the power generation module 20. Because the water pumps 84 are installed in each branch pipe 83, the amount of raw water supplied can be controlled for each power generation module 20 by independently controlling each water pump 84. An evaporator 25 is connected between the branch pipe 83 of the water supply system 80 and the fuel gas supply pipe 21a. The raw water is evaporated in the evaporator 25 and converted into steam.

[0084] In the EC mode, water vapor and a trace amount of hydrogen supplied by the water supply system 80 and the fuel supply system 40 are introduced as fuel gas into the fuel electrode of the fuel cell stack 21 via the fuel gas supply pipe 21a, and air supplied by the air supply system 50 is introduced as scavenging gas into the air electrode of the fuel cell stack 21 via the oxidant gas supply pipe 21b. When a power supply supplies a predetermined voltage between the terminals of the fuel cell stack 21 (reversible solid oxide cell stack) from a power source, the water vapor introduced into the fuel electrode is decomposed into hydrogen and oxygen ions (O ions) by electrolysis in the fuel electrode. 2-), oxygen is generated in the air electrode by the oxygen ions passing through the electrolyte. In addition, in this embodiment, a small amount of hydrogen is also supplied to the fuel electrode together with water vapor, so the fuel electrode is kept in a reducing atmosphere, which can suppress the oxidative degradation of the fuel electrode. The hydrogen generated by the fuel electrode is discharged as fuel electrode exhaust together with the water vapor that has not undergone electrolysis reaction, and is discharged to the outside of the module housing 29 after heat exchange with the water vapor supplied to the fuel electrode from the water supply system 80 in the heat exchanger 23. In addition, the fuel electrode exhaust containing hydrogen and water vapor is supplied to the circulation system 60 through the fuel electrode exhaust piping 62, and after being cooled and the water vapor is removed by the condenser 61 provided in the circulation system 60, it is stored in the hydrogen tank 2 through the collecting pipe 3 and the on-off valve 4. In addition, the on-off valve 4 is closed in the FC mode and opened in the EC mode. In addition, a part of the fuel electrode exhaust (hydrogen) passing through the condenser 61 is supplied to the burner 22 through the fuel electrode exhaust piping 63. On the other hand, the oxygen generated by the air electrode is directly supplied to the burner 22 as the air electrode exhaust together with the air passing through the air electrode. The combustion heat generated by the combustion of the mixed gas of the fuel electrode exhaust and the air electrode exhaust in the burner 22 is transferred to the evaporator 25. The evaporator 25 evaporates the water (raw water) supplied from the water supply system 80 to generate water vapor, and heats the generated water vapor. In addition, the burner 22 generates combustion exhaust gas, which is then heat-exchanged with the air supplied to the air electrode from the air supply system 50 in the heat exchanger 24, and then discharged to the outside air through the combustion exhaust gas piping 72 via the waste heat recovery system 70.

[0085] In the fuel cell system 10B of another embodiment configured in this manner, FC mode and EC mode can be switched and executed according to power demand. For example, when load L requires power, FC mode can be selected, while when load L does not require power, EC mode can be selected. Furthermore, in a fuel cell system 10B under a demand response contract, FC mode can be selected when a demand response (DR) is required to reduce power demand, while EC mode can be selected when a demand response (DR) is required to increase power demand.

[0086] In the above embodiment, although the unified control device 100 sets the hydrogen injection execution time and hydrogen injection execution flow rate of the fuel supply system 40 of each power generation module 20, each module control device 90 can also separately set the hydrogen injection execution time and hydrogen injection execution flow rate of the corresponding fuel supply system 40.

[0087] In the above embodiment, each of the plurality of power generation modules 20 included in the fuel cell system 10 includes one fuel cell stack 21. However, all or part of the plurality of power generation modules 20 may include a plurality of fuel cell stacks 21 connected in series or in parallel.

[0088] In the above-described embodiment, the fuel cell stacks 21 provided to the plurality of power generation modules 20 are connected in series with each other, but can be connected in parallel with each other.

[0089] In the above-described embodiment, the module control device 90 and the unified control device 100 are constituted by different control units, but can be constituted by a single control unit.

[0090] In the above-described embodiment, the fuel cell system 10 is provided with the plurality of power generation modules 20 each including the fuel cell stack 21, but can be provided with a single power generation module 20.

[0091] The above describes the mode for carrying out the present application using the embodiment, but the present application is not limited to such an embodiment, and of course can be carried out in various modes within the scope of the gist of the present application.

[0092] Further, in the present specification, the technical idea of changing "the fuel cell system according to claim 1" to "the fuel cell system according to any one of claims 1 to 5" is also disclosed in the initially filed technical solution 6.

[0093] [Possibility of use in industry]

[0094] The present application can be used in the manufacturing industry of fuel cell systems and the like.

[0095] Explanation of reference numerals

[0096] 10, 10B... fuel cell system, 20... power generation module, 21... fuel cell stack, 22... combustor (combustion section), 26... temperature sensor, 27... igniter, 29... module case (case), 30... auxiliary equipment, 40... fuel supply system, 50... air supply system (oxidizer gas supply system), 90... module control device (control section, individual control section), 100... unified control device (control section, unified control section).

Claims

1. A fuel cell system comprising: a fuel cell stack that generates electricity through the reaction of fuel gas and oxidant gas; a combustion unit that combusts a mixed gas of residual fuel gas and residual oxidant gas from the fuel cell stack; an igniter, which is used to ignite the combustion part; a housing having heat insulation properties and accommodating the fuel cell, the combustion unit, and the igniter; a fuel supply system for supplying fuel gas to the fuel cell stack; an oxidant gas supply system for supplying oxidant gas to the fuel cell stack; and A control unit, which supplies the above-mentioned oxidant gas when starting the system and performs a fuel pre-feeding process. In the fuel pre-feeding process, the above-mentioned fuel gas is supplied at a supply flow rate of the above-mentioned fuel gas so that the fuel concentration in the above-mentioned combustion unit becomes below the lower explosion limit relative to the supply flow rate of the above-mentioned oxidant gas, until the residual oxygen concentration in the fuel pipeline from the above-mentioned fuel supply system to the above-mentioned combustion unit becomes below a specified concentration, and then an ignition process for igniting the above-mentioned combustion unit is performed.

2. The fuel cell system according to claim 1, wherein: The above-mentioned control unit performs a first ignition process as the above-mentioned ignition process, and then performs a second ignition process. In the first ignition process, the above-mentioned fuel supply system and the above-mentioned oxidant gas supply system are controlled in a manner that the above-mentioned fuel gas and the above-mentioned oxidant gas are supplied to the above-mentioned combustion part within a range where the fuel concentration in the above-mentioned combustion part becomes below the lower explosion limit, and the above-mentioned igniter is controlled in a manner that the mixed gas of the above-mentioned fuel gas and the above-mentioned oxidant gas in the above-mentioned combustion part is ignited. In the second ignition process, the above-mentioned fuel supply system and the above-mentioned oxidant gas supply system are controlled in a manner that the above-mentioned fuel gas and the above-mentioned oxidant gas are supplied to the above-mentioned combustion part within a range where the fuel concentration in the above-mentioned combustion part becomes higher than the fuel concentration in the first ignition process and lower than the lower explosion limit.

3. The fuel cell system according to claim 2, wherein: A temperature sensor is provided to detect the temperature of the combustion portion. The above-mentioned control unit determines whether the above-mentioned first ignition process is successful or not based on the temperature of the combustion part detected by the above-mentioned temperature sensor in the above-mentioned first ignition process. When it is determined that the above-mentioned first ignition process has failed, before the above-mentioned first ignition process is successful, after purging the inside of the above-mentioned combustion part by supplying the above-mentioned oxidant gas, the flow rate of the fuel gas supplied to the above-mentioned combustion part is repeatedly increased and the processing of the above-mentioned first ignition process is executed again. If the above-mentioned first ignition process is not successful and the increased flow rate of the above-mentioned fuel gas exceeds the first upper limit value, the above-mentioned fuel cell system is stopped.

4. The fuel cell system according to claim 2, wherein: A temperature sensor is provided to detect the temperature of the combustion portion. The control unit determines whether the second ignition process is successful or not based on the temperature of the combustion unit detected by the temperature sensor in the second ignition process. If it is determined that the second ignition process has failed, the flow rate of the fuel gas supplied to the combustion unit is repeatedly increased and the second ignition process is executed again before the second ignition process succeeds. If the second ignition process is not successful and the increased flow rate of the fuel gas exceeds a second upper limit value, the fuel cell system is stopped. The second upper limit value is greater than the first upper limit value and is less than the lower explosion limit when converted to the fuel concentration of the burner.

5. The fuel cell system according to claim 3 or 4, wherein: A storage unit is provided for storing an incremental value of the fuel gas supplied when the first ignition step or the second ignition step is executed again. After stopping the fuel cell system, the control unit starts the first ignition process or the second ignition process at the next startup by increasing the supply flow rate of the fuel gas by the incremental value stored in the storage unit.

6. The fuel cell system according to claim 1, wherein: A plurality of power generation modules are provided, each including the fuel cell stack, the combustion unit, the igniter, the housing, the fuel supply system, and the oxidant gas supply system. Between the above-mentioned multiple power generation modules, each fuel cell stack is connected in series or in parallel. The fuel cell system further comprises: a plurality of individual control units for controlling auxiliary equipment of corresponding power generation modules among the plurality of power generation modules based on the instructions; A unified control unit supplies the oxidant gas when starting the fuel cell system and instructs the execution of a fuel pre-feeding process to the multiple individual control units. Thereafter, the unified control unit instructs the multiple individual control units to ignite the combustion unit. In the fuel pre-feeding process, the fuel gas is supplied at a fuel flow rate at which the fuel concentration of the combustion unit becomes below the lower explosion limit relative to the supply flow rate of the oxidant gas, until the residual oxygen concentration in the fuel pipeline from the fuel supply system to the combustion unit becomes below a specified concentration.

7. The fuel cell system according to claim 6, wherein: The unified control unit or the individual control unit obtains, in the fuel pre-feeding process, the amount of fuel required to replace the residual oxygen in the fuel pipeline with the fuel gas before the fuel concentration in the fuel pipeline of each power generation module becomes above the explosion upper limit as the required replacement amount in units of the power generation module, and sets the supply flow rate and supply time of the fuel gas of each power generation unit within the range where the fuel concentration in the combustion section becomes below the combustion lower limit relative to the supply flow rate of the oxidant gas based on the required replacement amount of each power generation module.

8. The fuel cell system according to claim 7, wherein: The unified control unit or the individual control unit sets the maximum value of the time obtained by dividing the required replacement amount of each power generation module by the flow rate of the fuel gas at which the fuel concentration of the combustion unit becomes below the combustion lower limit relative to the supply flow rate of the oxidant gas as the supply time shared by the multiple power generation modules, and sets the flow rate obtained by dividing the required replacement amount of each power generation module by the supply time as the supply flow rate of each power generation module.

9. The fuel cell system according to claim 7, wherein: The unified control unit or the individual control unit sets the flow rate of the fuel gas at which the fuel concentration of the combustion unit becomes below the combustion lower limit relative to the supply flow rate of the oxidant gas as the supply flow rate shared by the multiple power generation modules, and sets the time obtained by dividing the required replacement amount of each power generation module by the supply flow rate as the supply time of each power generation module.

10. The fuel cell system according to any one of claims 7 to 9, wherein: The unified control unit or the individual control unit measures the time elapsed after the fuel cell system is stopped, obtains the required replacement amount based on the elapsed time when the system is next started, and sets the supply flow rate and the supply time based on the required replacement amount.

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